Sequential Application of 1-naphthalenacetic Acid and Putrescine Promotes the Developmental Growth of Adventitious Roots in Chrysanthemum Cuttings

Chrysanthemums are among the most popular and economically valuable ornamental plants in the world. Herein, we investigated the effects of diamine putrescine (Put), a polyamine involved in plant cell differentiation and stress resistance, and 1-naphthaleneacetic acid (NAA), an auxin widely considered essential for root initiation, on the development of adventitious roots (ARs) and root systems in chrysanthemum cuttings. We also determined the optimal combination of concentrations of these treatments for AR developmental growth. When the cuttings were cultured with different concentrations of Put solutions, clear increases in AR length were recorded, although the number of ARs was unaffected. In addition, the number of lateral roots arising from ARs was increased by Put application. Treatment with 5-mg·L⁻¹ NAA in the first week followed by 100-mg·L⁻¹ Put in the next three weeks considerably increased the AR length compared with the use of each reagent alone. With the sequential application of 5-mg·L⁻¹ NAA and 200-mg·L⁻¹ Put, the fresh weight of the total roots that developed from the cuttings was increased by 6.05-fold compared with that without treatment. The superoxide dismutase activity and superoxide anion production rate were reduced in roots developed from Put-treated chrysanthemum cuttings. These results may indicate that Put application affected AR elongation by altering the quantitative balance among reactive oxygen species.